The clinical diagnoses in all 88 cases of monoclonal gammopathy, detected by general practitioners in Northern Jutland during a 3-year period, were investigated: 15% had malignant monoclonal gammopathy, 5% had non-haematologic cancers, and in 80% a benign disorder was found. These results indicate that the finding of a monoclonal gammopathy in general practice deserves attention, but it is rarely accompanied by a grave prognosis. Malignant monoclonal gammopathy should be suspected, but search for another type of cancer is not indicated.